BIOL 203 Microbiology LCC Exam 3 – Microbial Genetics, Metabolism & Control Mechanisms
What is the role of DNA in a cell? Two strands of DNA are held together by hydrogen bonds. Would a
covalent bond be a better option for holding the DNA strands together? Why or why not? Explain your
reasoning for full credit. - (ANSWER)What is DNA used for? Is there a time when a "weaker" bond would
be needed for DNA to carry out normal functions?
DNA is often described as the blueprints of a cell. It contains the instructions to make every single
protein the cell is able to make.
A covalent bond is considered a permanent bond. Two atoms share electrons. It is very strong and the
two atoms cannot easily be separated.
A hydrogen bond is an attraction between a partially positive and a partially negative atom or molecule.
This attraction while relatively weak in the case of one base pair, is very strong when taking into
consideration the additive effect of 1,000s, 100,000s, or even millions of base pairs that make up a
genome.
That means that as a whole, the DNA molecule is incredibly stable (a good trait for the molecule that
contains the blueprints of a cell!) while also being weak enough in small sections to be pulled apart for
the processes of replication and transcription.
What is a dogma? Describe the central dogma of biology. Include the names of the three cellular
molecules and the three processes that make those molecules in your description. - (ANSWER)What
processes are involved?
A dogma is a rule. The Central Dogma of Biology is the rule that governs information transfer in all living
things made up of cells. DNA to RNA to Protein. DNA is made via DNA in the process of replication, RNA
is made via DNA in the process of transcription, and protein is made via RNA in the process of
translation.
Other than topoisomerase and gyrase, name and describe the 6 enzymes/proteins used in DNA
replication of the leading strand. Are the same 6 enzymes/proteins used to replicate the lagging strand?
- (ANSWER)The 6 enzymes/proteins used in DNA replication of the leading strand are
, BIOL 203 Microbiology LCC Exam 3 – Microbial Genetics, Metabolism & Control Mechanisms
1. Helcase- This breaks the hydrogen bonds and makes them into two separate strands that will let other
enzymes to enter.
2. Single strand binding proteins- This binds to the newly separated single strands and makes them
stable enough to prevent them from bonding back together.
3. RNA primase- This gives DNA polymerase a 3' end to build form by putting down RNA primer.
4. DNA polymerase III- This synthesizes new DNA strands corresponding to the template strands that are
open.
5. DNA polymerase I- This removes the RNA primer nucleotides and puts DNA nucleotides in the oepn
space.
6. Ligase- This fills in the gaps in sugar-phosphate backbone.
The same 6 enzymes/proteins are used to replicate the lagging strand as well.
The lagging strand is replicated discontinuously (in Okazaki fragments.) Why is it not replicated
continuously like the leading strand? Be specific and use enzyme names and directionality in your
answer. - (ANSWER)What is the proper direction for DNA polymerase to work?
The parental strand that is used as the lagging strand template is in the 5' to 3' direction. DNA
polymerase needs a template that is 3' to 5' so that it can lay down nucleotides in the 5' to 3' direction.
Remember that enzymes are very specific as to what substrate will fit in the active site.
In order for DNA polymerase to replicate the lagging strand it must jump ahead and work backwards
putting the parental strand in the correct 3' to 5' orientation it needs.
This jumping ahead and working backwards creates many small fragments that must be linked together
by ligase.
What is the role of DNA in a cell? Two strands of DNA are held together by hydrogen bonds. Would a
covalent bond be a better option for holding the DNA strands together? Why or why not? Explain your
reasoning for full credit. - (ANSWER)What is DNA used for? Is there a time when a "weaker" bond would
be needed for DNA to carry out normal functions?
DNA is often described as the blueprints of a cell. It contains the instructions to make every single
protein the cell is able to make.
A covalent bond is considered a permanent bond. Two atoms share electrons. It is very strong and the
two atoms cannot easily be separated.
A hydrogen bond is an attraction between a partially positive and a partially negative atom or molecule.
This attraction while relatively weak in the case of one base pair, is very strong when taking into
consideration the additive effect of 1,000s, 100,000s, or even millions of base pairs that make up a
genome.
That means that as a whole, the DNA molecule is incredibly stable (a good trait for the molecule that
contains the blueprints of a cell!) while also being weak enough in small sections to be pulled apart for
the processes of replication and transcription.
What is a dogma? Describe the central dogma of biology. Include the names of the three cellular
molecules and the three processes that make those molecules in your description. - (ANSWER)What
processes are involved?
A dogma is a rule. The Central Dogma of Biology is the rule that governs information transfer in all living
things made up of cells. DNA to RNA to Protein. DNA is made via DNA in the process of replication, RNA
is made via DNA in the process of transcription, and protein is made via RNA in the process of
translation.
Other than topoisomerase and gyrase, name and describe the 6 enzymes/proteins used in DNA
replication of the leading strand. Are the same 6 enzymes/proteins used to replicate the lagging strand?
- (ANSWER)The 6 enzymes/proteins used in DNA replication of the leading strand are
, BIOL 203 Microbiology LCC Exam 3 – Microbial Genetics, Metabolism & Control Mechanisms
1. Helcase- This breaks the hydrogen bonds and makes them into two separate strands that will let other
enzymes to enter.
2. Single strand binding proteins- This binds to the newly separated single strands and makes them
stable enough to prevent them from bonding back together.
3. RNA primase- This gives DNA polymerase a 3' end to build form by putting down RNA primer.
4. DNA polymerase III- This synthesizes new DNA strands corresponding to the template strands that are
open.
5. DNA polymerase I- This removes the RNA primer nucleotides and puts DNA nucleotides in the oepn
space.
6. Ligase- This fills in the gaps in sugar-phosphate backbone.
The same 6 enzymes/proteins are used to replicate the lagging strand as well.
The lagging strand is replicated discontinuously (in Okazaki fragments.) Why is it not replicated
continuously like the leading strand? Be specific and use enzyme names and directionality in your
answer. - (ANSWER)What is the proper direction for DNA polymerase to work?
The parental strand that is used as the lagging strand template is in the 5' to 3' direction. DNA
polymerase needs a template that is 3' to 5' so that it can lay down nucleotides in the 5' to 3' direction.
Remember that enzymes are very specific as to what substrate will fit in the active site.
In order for DNA polymerase to replicate the lagging strand it must jump ahead and work backwards
putting the parental strand in the correct 3' to 5' orientation it needs.
This jumping ahead and working backwards creates many small fragments that must be linked together
by ligase.
